The detailed geometrical and electronic structures of monoclinic zirconia Original Research Article

The detailed geometrical and orbital-decomposed electronic structures of monoclinic ZrO2 have been investigated by using the first-principle projector augmented wave (PAW) potential within the generalized gradient approximation as well as taking into account on-site Coulomb repulsive interaction (GGA+U ). The optimized structure shows the OI atom locates slightly outside the plane of an arbitrary triangle formed by three coordinated Zr atoms and the OII atom is inside an arbitrary tetrahedron formed by four coordinated Zr atoms; in turn, the Zr atom is surrounded by an arbitrary decahedron formed by seven oxygen ligands. Compared to OI atom coordinated to three Zr atoms in an almost planar environment, one more coordinated Zr atom and thus an arbitrary tetrahedron environment of total four coordinated Zr atoms makes density of states (DOS) of s and three p (px, py and pz) states of the OII atom not only shift toward lower energy region but also drive down in higher energy region and drive up in lower energy region. No crystal-field splitting is observed among three p (px, py and pz) states of anions OI and OII as well as among three p (px, py and pz) states and five d (dxy, dyz, dxz, d2zdz2 and d2x−2ydx2−y2) states of cation Zr as the arrangements of the surrounding cations (anions) do not have any symmetry. The additional covalent character of Zr–O ionic bonds is attributed to the hybridization of itinerant Zr(5s) and less filled Zr(4d) states to the separated O(2s) and O(2p) states.